I am hardly an expert but I search the Net daily and this is based on what I've learned in the last couple of years.

Search engines do vary but this is basically what they are and how they work.How do search engines search?

Contrary to popular belief, search engines don't "search the Web" when you insert a word or phrase. They search an index already created at their site.

An actual Web-search engine is built by their finding Web pages, copying them, filing them at their site and then those pages are indexed, waiting for you to feed in a word or phrase. When you do, it accesses the index that is now stored at their site and gives you the results. This is why they can work so fast.

The extent of a search by a search engine is thus proportional to the number of pages/sites that they have copied, saved and indexed. How it presents the information to you is based on their software amd varies between sites.

Given the size of the Web, storing pages can be, of course, staggering. Google, for example, says it is storing nearly 1.4 billion - yes, billion - Web pages at this writing. It will increase.How do they select or rank the pages?

When you get the result of your search, the suggested pages are presented in a certain order. Do the same search at another site and they will come up in a different order. So how do they select the order? Well, the answer is complex, controversial and incomplete.

Some search engines go by the number of times that word appears on the page and/or how high the word is on the page. If the word is in the title of the document, it will count more than if it is down towards the bottom. If it appears 10 times, it is worth more than one time. Go figure, but it was the best that some could do at the time.

Others go by how many sites link to that page and/or how often it is accessed.

So the page you may really want could be at the bottom of their list. That is why a good engine is really crucial, to allow you to modify your search and really narrow it down because you can't rely on the order the search engine gives you and you may not have time to go through 5,000 pages.Types of sites and two types again

There are basically two types of search sites: search engines and directories. For each, they can be broken down further as generic (any topic) and specific (they specialize.)

If you want to know if there is a search engine/directory for a particular topic, go to the guide to search engines that lets you look at
http://www.searchengineguide.com/searchengines.html. Just remember, they only guide you to search engines/directories and don't actual search the Web.

It has limits. Feeding "prostate cancer" to Search Engine Guide produces only one site, HealthLink
which turned out to be a broken link. Additionally, there are PCa sites that Search Engine Guide doesn't list, such as the resources at National Cancer Institute.A different type of search: via images

There are now IMAGE search engines that allow you to search for an image. This can be an innovative way to find something because you come in via a visual. There is:

Why would you search for an image? Well, try "prostate gland" in Google and you will find drawings, photos and slides. You will also get more junk as it is not as precise. Doing the same in Ditto produces hardly anything, by comparison.Other types of search engines: meta

There are search engines that try to give a "human interface" where you type in a question. "Ask Jeeves" is one of the more popular ones at
http://www.ask.com/index.asp?
It is a comfortable way to learn to prowl the Web but it has limits. It also gets confused. Asking "What are the signs of prostate cancer?" offered me advice for the astrological sign of Cancer, as well as suggesting some sites more relevant to my request.

Ask Jeeves is an example of a META-search engine. It taps into other search engines. This sound good but don't expect the best service.

There is more information out there than one can imagine. The trick is knowing how to find it and the ONLY way to find YOUR search engine is to test them and THEN learn how to use them for some have special features that allow you to really narrow it down. (See the Primer on how to narrow down.)